EP1797060A2 - "process for preparation of citalopram and enantiomers" - Google Patents

"process for preparation of citalopram and enantiomers"

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Publication number
EP1797060A2
EP1797060A2 EP05815687A EP05815687A EP1797060A2 EP 1797060 A2 EP1797060 A2 EP 1797060A2 EP 05815687 A EP05815687 A EP 05815687A EP 05815687 A EP05815687 A EP 05815687A EP 1797060 A2 EP1797060 A2 EP 1797060A2
Authority
EP
European Patent Office
Prior art keywords
formula
compound
dimethylamino
fluorophenyl
group
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05815687A
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German (de)
French (fr)
Inventor
Nagarajan Sun Pharma Adv. Res. Centre PERIYANDI
Srinivasu Sun Pharma Adv. Res. Centre KILARU
Rajamannar Sun Pharma Adv. Res. Centre THENNATI
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Sun Pharma Global FZE
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Sun Pharmaceutical Industries Ltd
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Publication date
Application filed by Sun Pharmaceutical Industries Ltd filed Critical Sun Pharmaceutical Industries Ltd
Priority to EP09172751A priority Critical patent/EP2141156A1/en
Publication of EP1797060A2 publication Critical patent/EP1797060A2/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C255/00—Carboxylic acid nitriles
    • C07C255/49—Carboxylic acid nitriles having cyano groups bound to carbon atoms of six-membered aromatic rings of a carbon skeleton
    • C07C255/58—Carboxylic acid nitriles having cyano groups bound to carbon atoms of six-membered aromatic rings of a carbon skeleton containing cyano groups and singly-bound nitrogen atoms, not being further bound to other hetero atoms, bound to the carbon skeleton
    • C07C255/59—Carboxylic acid nitriles having cyano groups bound to carbon atoms of six-membered aromatic rings of a carbon skeleton containing cyano groups and singly-bound nitrogen atoms, not being further bound to other hetero atoms, bound to the carbon skeleton the carbon skeleton being further substituted by singly-bound oxygen atoms
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
    • C07D307/77—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom ortho- or peri-condensed with carbocyclic rings or ring systems
    • C07D307/78—Benzo [b] furans; Hydrogenated benzo [b] furans
    • C07D307/79—Benzo [b] furans; Hydrogenated benzo [b] furans with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to carbon atoms of the hetero ring
    • C07D307/81—Radicals substituted by nitrogen atoms not forming part of a nitro radical
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
    • C07D307/77—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom ortho- or peri-condensed with carbocyclic rings or ring systems
    • C07D307/87—Benzo [c] furans; Hydrogenated benzo [c] furans

Definitions

  • the invention provides a process for preparation of (RS)-( ⁇ )-l-[3- (dimethylamino)propyl]- 1 -(4-fluorophenyl)- 1 ,3-dihydro-5-isobenzofuran carbonitrile (a compound of formula I, BSfN name for the compound is citalopram) and its enantiomers viz.
  • the invention provides a process for preparation of citalopram or its enantiomers via novel ether intermediate compounds.
  • Citalopram was first disclosed in United States Patent No. 4136193 and (S)-(+> citalopram in USRE 34712 (the '712 patent).
  • United States Patent No. 4650884 teaches use of the diol, viz., 4-[4 ⁇ (dimethylamino)-l- (4-fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, a compound of formula IV in racemic form, which is cyclized in presence Of H 2 SO 4 to obtain citalopram (Scheme I).
  • the '712 patent teaches preparation of (S)-(+)-citalopram, a compound of formula II by using the enantiomeric diol compound of formula IV, viz., (S)-(-)-4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- l-butyl]-3-(hydroxymethyl)-benzonitrile, which is derivatized to obtain a labile ester thereof like methanesulfonyl, p-toluenesulfonyl, 10- camphorsulfonyl, trifluoroacetyl or trifluoromethanesulfonyl.
  • the labile ester derivative is cyclized stereoselectively, in presence of a base to obtain the (+)-isomer, namely (S)- (+)-citalopram (Scheme II).
  • labile esters demonstrated for making enantiomers of citalopram requires use of a reactive agents like methanesulfonyl chloride which could give rise bismesylates and thus could lead to the formation of undesired impurities.
  • organic bases like triethylamine, pyridine are used as proton scavengers, the undesired labile esters of tertiary alcohol group formed under the reaction condition can proceed via non-concerted manner resulting in chirality perturbation and impurity formation.
  • the excess of base employed can also participate in displacing the reactive ester to form the corresponding ammonium derivatives due to its inherent nucleophilicity.
  • the labile ester is sensitive to moisture, temperature, resulting in decomposition.
  • the present invention provides such a process for preparation of citalopram and enantiomers thereof by use of the racemic or enantiomeric diol intermediate, which is derivatized to obtain an ether derivative thereof, which can be cyclised in-situ to obtain citalopram or enantiomers thereof.
  • the ether derivatives are formed at the primary alcohol group of the diol intermediate by reacting with aryls, het ⁇ roaryls or alkyls optionally substituted with electron withdrawing groups.
  • the present invention provides a process for preparation of citalopram or enantiomers thereof, particularly, (S)-(+)-citalopram of desired enantiomeric purity.
  • the present invention provides a process for preparation of l-[3-(dimethylamino)propyl]- l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting a compound of formula IVa, in the presence of a base with a compound of formula RX,
  • R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR 1 , wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group; further wherein RX is selected such that an intermediate ether derivative, a compound of formula Va formed from said reaction cyclizes to a compound of formula VI,
  • Formula Va Formula VI and where Z is not a cyano group, conversion of the group Z in the compound of formula VI to a cyano group to form l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3- dihydro-5-isobenzofuran carbonitrile.
  • the present invention in one embodiment provides a process for preparation of l-[3- (dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting 4- [4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 - (hydroxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl 5 Br, I, CN, OTf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R] is optionally substituted alkyl; further wherein RX is selected such that an intermediate ether derivative, a compound of formula V formed from said reaction,
  • Formula V cyclizes to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile.
  • the present invention provides novel ether compound, a compound of formula Va, or acid addition salt thereof,
  • R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and Z is a cyano group or a group that may be converted to a cyano group.
  • the present invention in one embodiment provides novel ether compound, a compound of formula V or acid addition salt thereof,
  • R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups.
  • the present invention provides a process for preparation of a compound of formula Va, comprising reacting a compound of formula IVa, in the presence of a base with a compound of formula RX,
  • Formula IVa Formula Va wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR], wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group.
  • the present invention in one embodiment provides a process for preparation , of a compound of formula V,
  • Formula V comprising reacting 4- [4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 - (hydiOxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R 1 is optionally substituted alkyl.
  • l-[3-(dimemylamino)propyl]-l -(4-fluorophenyl)- l,3-dihydro-5- isobenzofuran carbonitrile may represent a racemic or an enantiomeric compound, especially (S)-(+)-isomer thereof, unless otherwise specified.
  • the compound of formula IVa, the compound of formula Va or the compound of formula VI represents a racemic or an enantiomeric compound, unless otherwise specified.
  • Z is a cyano group or a group that may be converted to a cyano group.
  • groups, Z may be selected from halogen, -OH, -CHO, -CH 2 OH, -CH 2 NH 2 , -CH 2 NO 2 , -CH 3 , -CH 2 Cl, -CH 2 Br, -NHR 2 , -COOR 3 , -CONR 3 R 4 , CF 3 -(CF 2 ) n -SO 2 -O- wherein n is 0-8, R 2 is hydrogen or Cl to C6 alkylcarbonyl and R 2 and R 3 are selected from hydrogen, optionally substituted Cl to C6 alkyl or aryl and, a group of formula VII:
  • conversion of the compound of formula VI to form l ⁇ [3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile may be carried out by any process as known in the art, for example as described in United States Patent No. 4136193, PCT publications WO 00/13648, WO 00/11926 or WO 01/02383.
  • the compound RX is a compound, which can react with a compound of formula IVa such as, 4-[4-(dimethylamino)-l-(4-fluorophenyl)-l-hydroxy-l-butyl]-3-
  • RX is a compound of formula, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R 1 is alkyl optionally substituted with electron withdrawing groups.
  • RX is further selected from compounds capable of forming an ether derivative, a compound of formula Va.
  • a compound of formula Va is formed by reaction of compound of formula IVa with a compound of formula RX, in presence of a base.
  • the compound of formula Va can in-situ cyclize to form a compound of formula VI. If desired it can be isolated and then subjected to cyclization in presence of a base.
  • the ether derivative compound of formula V formed by reaction of 4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl]-3-
  • the compound RX is not labile like methanesulfonyl chloride used in the prior art, the '712 patent, and thus resulting in an advantage of easier handling and - storage and leading to preparation of chirally pure S-(+)-citalopram end product.
  • the use of methanesulfonyl chloride may give rise to bismesylates leading to formation of undesired impurities with chirality perturbation.
  • the present invention provides novel ether compound, a compound of formula Va, or acid addition salt thereof,
  • Formula IVa Formula Va and a process for preparation thereof comprising reacting a compound of formula IVa, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi 5 wherein Tf represents trifluoromethanesulfonyl group, and R 1 is optionally substituted alkyl, Z is a cyano group or a group that maybe converted to a cyano group.
  • RX is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi 5 wherein Tf represents trifluoromethanesulfonyl group, and R 1 is optionally substituted alkyl, Z is a cyano group or a
  • the present invention in one embodiment provides novel ether compound, a compound of formula V, or acid addition salt thereof,
  • Formula V and a process for preparation thereof comprising reacting 4-[4-(dimethylamino)-l-(4- fluorophenyl)-l -hydroxy- 1 -butyl] -3 -(hydroxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR] , wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl.
  • RX wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR] , wherein Tf represents trifluoromethanesulfonyl group, and
  • the present invention provides 4-[4-(dimethylamino)-l-(4- fluorophenyl)- 1 -hydroxy- 1 -butyl]-3 -(2-nitro-4-chlorophenoxymethyl)-benzonitrile, a compound of formula VIE, or acid addition salt thereof,
  • Formula VIII and a process for preparation thereof comprising reacting 4-[4-(dimethylamino)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, in the presence of a base, with 2,5-dichloronitrobenzene.
  • the present invention provides novel (S)-4-[4- (dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(2-nitro-4-chlorophenoxy- methyl)-benzonitrile or an acid addition salt thereof for example, hydrochloride salt.
  • the present invention provides (S)-(-)-4-[4- (dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(2-nitro-4-chlorophenoxy- methyl)-benzonitrile hydrochloride.
  • the acid addition salt of compound of formula V, Va or VEI may be prepared by any standard method of contacting the compound of formula V, Va or VIII with an acid, for example inorganic acid like hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like or organic acid like oxalic acid, citric acid, succinic acid, cinnamic acid, p-toluenesulfonic acid and the like.
  • an acid for example inorganic acid like hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like or organic acid like oxalic acid, citric acid, succinic acid, cinnamic acid, p-toluenesulfonic acid and the like.
  • alkyl may be any straight, branched, or cyclic alkyl group of Cl to C6 atoms, optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4-bis(trifluoroalkyl), 2,6-bis(trifluoroalkyl), -CHO, -COOR 9 , wherein R9 may be alkyl, aryl or heteroaryl.
  • alkenyl may be any straight, branched, or cyclic alkyl group of Cl to C6 atoms, optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4-bis(trifluoroalkyl), 2,6-bis(trifluoroalkyl), - CHO, -COOR 9 , wherein R9 may be alkyl, aryl or heteroaryl.
  • aryl may be a mono-, bi- or polycyclic aromatic system, for example phenyl, naphthyl, optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4-bis(trifiuoroalkyl) or 2,6- bis(trifluoroalkyl), -CHO, -COOR 9 , wherein R 9 may be alkyl, aryl or heteroaryl.
  • heteroaryl may be a mono-, bi- or polycyclic aromatic system containing one or more hetero atom which may be same or different, for example quinolinyl, isoquinolinyl, pyridinyl, indanyl, fluorenyl, oxazolyl, pyrazinyl, thienyl, quinazolinyl, benzimidazolyl and the like optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4- bis(trifluoroalkyl) or 2,6-bis(trifluoroalkyl), -CHO, -COOR 9 , wherein Rg may be alkyl, aryl or heteroaryl.
  • hetero atom may preferably be selected from N, O, S or P,
  • the base used may be selected from an alkoxide, wherein the alkyl residue is Cl to C6 linear, branched or cyclic alkyl and the counter ion is an alkali or alkaline earth metal; alkali or alkaline earth metal oxide, hydroxide, carbonate or bicarbonate or an amine base.
  • the amine base may be selected from aliphatic or aromatic amines, cyclic or acyclic amines, for example isoquino lines, quino lines, dialkylarylamines, pyridine, substituted pyridines.
  • the base may be selected from moderate bases that do not favor the formation of bisalkoxides thus providing control over the derealization of the primary alcohol group of the diol.
  • the ether derivative compounds represented by a compound of formula V or Va can cyclize to form citalopram or enantiomers thereof.
  • the diol compound viz., a compound of formula IV or IVa is used in enantiomeric form, derivatized to form an ether derivative thereof, a compound of formula V or Va, it cyclizes stereoselectively to afford enantiomerically pure citalopram.
  • the group R is:
  • P and Q may be selected from electron withdrawing groups like NO 2 , CF 3 , CN, halogen, COOR 9 , CHO and the like, wherein R 9 is alkyl, aryl or heteroaryl.
  • the present invention provides a process for preparation of racemic l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting racemic 4-[4-(dimethylamino)-l-(4-fluorophenyl)-l- liydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile 5 with a compound of formula RX, in presence of a base.
  • the compound of formula RX is dichloronitrobenzene.
  • the present invention provides a process for preparation of enantiomeric l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile comprising reacting enantiomeric 4-[4-(dimethylammo)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, with a compound of formula RX, in presence of a base.
  • the compound of formula RX is dichloronitrobenzene.
  • the present invention provides a process for preparation of (S)-(+)- 1 -[3-(dimethylammo) ⁇ ropyl] - 1 -(4-fluorophenyl)- 1 ,3 -dihydro-5 -isobenzofuran carbonitrile comprising reacting (S)-(-)-4-[4-(dimethylamino)-l -(4-fluorophenyl)- 1- hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, with a compound of formula RX, in presence of a base.
  • the compound of formula RX is dichloronitrobenzene.
  • the present invention provides a process for preparation of (S)-(+)-l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile comprising reacting (S)-(-)-4-[4-(dimethylamino)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile with 2,5- dichloronitrobenzene, in presence of a base to form a compound of formula VHt,
  • the process of the present invention may be carried out in any suitable solvent.
  • solvents that may be used are alcohol solvents like methanol, ethanol, t-butanol, polyethyleneglycol; ketone solvents like acetone, methyl iso-butyl ketone; ether solvents like tetrahydrofuran, dioxane; ester solvents like ethylacetate, butylacetate; amide solvents like dimethylformamide, dimethylacetamide; nitrile solvents like acetonitrile; dipolar aprotic solvents like dimethylsulfoxide, sulfolane; hydrocarbon and aromatic hydrocarbon solvents having a boiling point greater than 70°C.
  • the process of the present invention can be carried out in a suitable solvent with a base at temperature ranging from ambient to the reflux temperature of the selected solvent.
  • the reaction may be completed in 0.5 to 40 hours, preferably 0.5 to 20 hours depending on the selected solvent and base.
  • the reaction may be worked-up by quenching by addition of 2 to 10 volumes, preferably 3 to 8 volumes of water to the reaction solvent, depending on the product solubility in the selected solvent, at temperature between the range of O 0 C to 100°C, preferably 20°C to 60 0 C.
  • the reaction mixture may be extracted with a suitable water-immiscible solvent like toluene, ether, ethylacetate.
  • 1 -[3-(dimethylamino)propyl]- 1 -(4-fluorophenyl)- 1 ,3-dihydro-5-isobenzofuran carbonitrile may be converted to a pharmaceutically acceptable acid addition salt thereof by treatment with organic or inorganic acid.
  • organic acids are oxalic, fumaric, succinic mandelic, benzoic, p-toluenesulfonic acid and the like.
  • inorganic acids are hydrobromic, hydrochloric, sulfuric, phosphoric, nitric and the like.
  • the preparation of salt formation may be carried out in a solvent like acetone, water, methanol, isopropanol, dimethylformamide or mixture thereof.
  • the dichloromethane layer was washed with water and distilled and dissolved the material in toluene, the toluene layer was washed with water and distilled to get an oily product.
  • the oil was dissolved in 50 ml acetone and 5.12 gm of oxalic acid dihydrate in 50 ml acetone was added to it at room temperature, stirred and cooled.
  • Experiments A(2) and A(3) have been carried out in similar way as in Experiment No. A(I). Comparative Experiments A(I), A(2) and A(3) have been carried out according to the teaching of prior art, United States Patent No. Re 34712, which is incorporated herein by reference.

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Abstract

The present invention provides a process for preparation of l-[3-(dimethylamino)propyl]- l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting a compound of formula (Iva), in the presence of a base with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, Otf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R1 is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group; further wherein RX is selected such that an intermediate ether derivative, a compound of formula (Va) formed from said reaction cyclizes to a compound of formula (VI), and where Z is not a cyano group, conversion of the group Z in the compound of formula (VI) to a cyano group to form l-[3-(dimethylamino)ρropyl]-l-(4-fluoroρhenyl)-l,3-dihydro-5-isobenzofuran carbonitrile. The present invention also provides novel ether compound, a compound of formula (Va) and a process for preparation thereof.

Description

Process for preparation of citalopram and enantiomers
The invention provides a process for preparation of (RS)-(±)-l-[3- (dimethylamino)propyl]- 1 -(4-fluorophenyl)- 1 ,3-dihydro-5-isobenzofuran carbonitrile (a compound of formula I, BSfN name for the compound is citalopram) and its enantiomers viz. , (S)-(+)- 1 - [3 -(dimethylamino)propyl] - 1 -(4-fluorophenyl)- 1 ,3 -dihydro-5 - isobenzofuran carbonitrile (a compound of formula π, known as (S)-(+)-citalopram or escitalopram) and (R)-(-)- 1 -[3-(dimethylamino)propyl]- 1 -(4-fluorophenyl)- 1 ,3-dihydro- 5-isobenzofuran carbonitrile (a compound of formula El) and acid addition salts thereof.
(RS) (S) (R)
Formula I Formula II Formula III
More particularly, the invention provides a process for preparation of citalopram or its enantiomers via novel ether intermediate compounds.
Citalopram was first disclosed in United States Patent No. 4136193 and (S)-(+> citalopram in USRE 34712 (the '712 patent).
United States Patent No. 4650884 teaches use of the diol, viz., 4-[4~(dimethylamino)-l- (4-fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, a compound of formula IV in racemic form, which is cyclized in presence Of H2SO4 to obtain citalopram (Scheme I).
Formula IV Formula I
Scheme I
The '712 patent teaches preparation of (S)-(+)-citalopram, a compound of formula II by using the enantiomeric diol compound of formula IV, viz., (S)-(-)-4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- l-butyl]-3-(hydroxymethyl)-benzonitrile, which is derivatized to obtain a labile ester thereof like methanesulfonyl, p-toluenesulfonyl, 10- camphorsulfonyl, trifluoroacetyl or trifluoromethanesulfonyl. The labile ester derivative is cyclized stereoselectively, in presence of a base to obtain the (+)-isomer, namely (S)- (+)-citalopram (Scheme II).
Scheme II The prior art strategies are based on cyclization of the diol under acidic conditions to obtain citalopram or derivatization through a labile ester derivative and cyclization in presence of a base to obtain (S)-(+)-citalopram. These processes of prior art have following disadvantages when the process is to be scaled-up for industrial use: 1. Cyclization of the diol at higher temperature using acids generates amide, acid, indene by-products leading to formation of impure product.
2. Use of the labile esters demonstrated for making enantiomers of citalopram requires use of a reactive agents like methanesulfonyl chloride which could give rise bismesylates and thus could lead to the formation of undesired impurities. 3. For preparation of the labile esters, organic bases like triethylamine, pyridine are used as proton scavengers, the undesired labile esters of tertiary alcohol group formed under the reaction condition can proceed via non-concerted manner resulting in chirality perturbation and impurity formation. The excess of base employed can also participate in displacing the reactive ester to form the corresponding ammonium derivatives due to its inherent nucleophilicity.
4. The labile ester is sensitive to moisture, temperature, resulting in decomposition.
There is a need for a convenient, robust process for efficient preparation of citalopram and enantiomers thereof. The present invention provides such a process for preparation of citalopram and enantiomers thereof by use of the racemic or enantiomeric diol intermediate, which is derivatized to obtain an ether derivative thereof, which can be cyclised in-situ to obtain citalopram or enantiomers thereof. The ether derivatives are formed at the primary alcohol group of the diol intermediate by reacting with aryls, hetέroaryls or alkyls optionally substituted with electron withdrawing groups.
The present invention provides a process for preparation of citalopram or enantiomers thereof, particularly, (S)-(+)-citalopram of desired enantiomeric purity. SUMMARY OF THE PRESENT INVENTION
The present invention provides a process for preparation of l-[3-(dimethylamino)propyl]- l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting a compound of formula IVa, in the presence of a base with a compound of formula RX,
Formula IVa wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR1, wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group; further wherein RX is selected such that an intermediate ether derivative, a compound of formula Va formed from said reaction cyclizes to a compound of formula VI,
Formula Va Formula VI and where Z is not a cyano group, conversion of the group Z in the compound of formula VI to a cyano group to form l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3- dihydro-5-isobenzofuran carbonitrile. The present invention in one embodiment provides a process for preparation of l-[3- (dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting 4- [4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 - (hydroxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl5 Br, I, CN, OTf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R] is optionally substituted alkyl; further wherein RX is selected such that an intermediate ether derivative, a compound of formula V formed from said reaction,
Formula V cyclizes to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile.
The present invention provides novel ether compound, a compound of formula Va, or acid addition salt thereof,
Formula Va wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and Z is a cyano group or a group that may be converted to a cyano group.
The present invention in one embodiment provides novel ether compound, a compound of formula V or acid addition salt thereof,
Formula V wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups.
The present invention provides a process for preparation of a compound of formula Va, comprising reacting a compound of formula IVa, in the presence of a base with a compound of formula RX,
Formula IVa Formula Va wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR], wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group. The present invention in one embodiment provides a process for preparation , of a compound of formula V,
Formula V comprising reacting 4- [4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 - (hydiOxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R1 is optionally substituted alkyl.
DETAILS OF THE PRESENT INVENTION
As used herein l-[3-(dimemylamino)propyl]-l -(4-fluorophenyl)- l,3-dihydro-5- isobenzofuran carbonitrile may represent a racemic or an enantiomeric compound, especially (S)-(+)-isomer thereof, unless otherwise specified.
The compound of formula IVa, the compound of formula Va or the compound of formula VI represents a racemic or an enantiomeric compound, unless otherwise specified.
Z is a cyano group or a group that may be converted to a cyano group. Such groups, Z, may be selected from halogen, -OH, -CHO, -CH2OH, -CH2NH2, -CH2NO2, -CH3, -CH2Cl, -CH2Br, -NHR2, -COOR3, -CONR3R4, CF3-(CF2)n-SO2-O- wherein n is 0-8, R2 is hydrogen or Cl to C6 alkylcarbonyl and R2 and R3 are selected from hydrogen, optionally substituted Cl to C6 alkyl or aryl and, a group of formula VII:
Formula VII wherein Y is O or S; R5 and R6 are each independently selected from hydrogen and Cl to C6 alkyl or R5 and R6 together form a C2 to C5 alkylene chain thereby forming a spiro ring; R7 is selected from hydrogen, Cl to C6 alkyl, Rg is selected from hydrogen, Cl to C6 alkyl, a carboxy group or a precursor group thereof, or R7 and R8 together form a C2 to C5 alkylene chain thereby forming a spiro ring.
When Z is halogen, in particular bromo or chloro, conversion of the compound of formula VI to form l~[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile may be carried out by any process as known in the art, for example as described in United States Patent No. 4136193, PCT publications WO 00/13648, WO 00/11926 or WO 01/02383.
Compounds of formula VI, wherein the group Z is CF3-(CF2)n-SO2-O-, wherein n is 0-8, may be converted to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile by methods analogous to those described in PCT publication WO 00/13648.
Compounds of formula VI, wherein the group Z is -CHO, may be converted to l-[3-
(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile by methods analogous to those described in PCT publication WO 99/30548.
Compounds of formula VI, wherein the group Z is -NHR2, wherein R2 is hydrogen or alkylcarbonyl, may be converted by to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)- l,3-dihydro-5-isobenzofuran carbonitrile by methods analogous to those described in PCT publication WO 98/19512.
Compounds of formula VI, wherein the group Z is -COOR3 or -CONR3R4, wherein R3 and R4 are selected from hydrogen and optionally substituted alkyl or aryl may be converted to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile by methods analogous to those described in PCT publications WO 98/19511 and WO 98/19513.
Compounds of formula VI, wherein the group Z is a group of formula VII may be converted to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile by methods analogous to those described in PCT publication WO 00/23431.
Compounds of formula VI, wherein Z is OH, -CH2OH, -CH2NH2, -CH2NO2, -CH2Cl, -CH2Br, -CH3 or any of the groups above, may be converted to l-[3- (dimethylamino)propyl] - 1 -(4-fluorophenyl)- 1 ,3 -dihydro-5-isobenzofuran carbonitrile by methods analogous to those described in PCT publications WO 01/68632 and WO
01/85712.
Starting materials of formula FVa may be prepared according to the above mentioned patents and patent applications, which are incorporated herein by reference or by analogous methods known in the art.
The compound RX is a compound, which can react with a compound of formula IVa such as, 4-[4-(dimethylamino)-l-(4-fluorophenyl)-l-hydroxy-l-butyl]-3-
(hydroxymethyl)-benzonitrile to form a ether derivative, a compound of formula Va, via addition-elimination type reaction, X being any suitable leaving group. A suitable leaving group is any group which upon reaction of a compound of formula IVa with the compound RX, facilitates formation of an ether derivative represented by a compound of formula Va. In a preferred embodiment RX is a compound of formula, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi, wherein Tf represents trifluoromethanesulfonyl group, and R1 is alkyl optionally substituted with electron withdrawing groups.
RX is further selected from compounds capable of forming an ether derivative, a compound of formula Va.
hi the process of the invention, a compound of formula Va is formed by reaction of compound of formula IVa with a compound of formula RX, in presence of a base. The compound of formula Va can in-situ cyclize to form a compound of formula VI. If desired it can be isolated and then subjected to cyclization in presence of a base.
In a preferred embodiment, the ether derivative compound of formula V, formed by reaction of 4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl]-3-
(hydroxymethyl)-benzonitrile with a compound of formula RX, in presence of a base, cyclizes in-situ to directly form l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3- dihydro-5-isobenzofuran carbonitrile. However, if it is so desired, the ether derivative compound of formula V may be isolated and subjected to cyclization in presence of a base.
Further, preferably, the compound RX is not labile like methanesulfonyl chloride used in the prior art, the '712 patent, and thus resulting in an advantage of easier handling and - storage and leading to preparation of chirally pure S-(+)-citalopram end product. The use of methanesulfonyl chloride may give rise to bismesylates leading to formation of undesired impurities with chirality perturbation.
The present invention provides novel ether compound, a compound of formula Va, or acid addition salt thereof,
Formula IVa Formula Va and a process for preparation thereof comprising reacting a compound of formula IVa, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and ORi5 wherein Tf represents trifluoromethanesulfonyl group, and R1 is optionally substituted alkyl, Z is a cyano group or a group that maybe converted to a cyano group.
The present invention in one embodiment provides novel ether compound, a compound of formula V, or acid addition salt thereof,
Formula V and a process for preparation thereof comprising reacting 4-[4-(dimethylamino)-l-(4- fluorophenyl)-l -hydroxy- 1 -butyl] -3 -(hydroxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR] , wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl. In a preferred embodiment, the present invention provides 4-[4-(dimethylamino)-l-(4- fluorophenyl)- 1 -hydroxy- 1 -butyl]-3 -(2-nitro-4-chlorophenoxymethyl)-benzonitrile, a compound of formula VIE, or acid addition salt thereof,
Formula VIII and a process for preparation thereof comprising reacting 4-[4-(dimethylamino)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, in the presence of a base, with 2,5-dichloronitrobenzene.
In a more preferred embodiment, the present invention provides novel (S)-4-[4- (dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(2-nitro-4-chlorophenoxy- methyl)-benzonitrile or an acid addition salt thereof for example, hydrochloride salt.
hi a particularly preferred embodiment, the present invention provides (S)-(-)-4-[4- (dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(2-nitro-4-chlorophenoxy- methyl)-benzonitrile hydrochloride.
The acid addition salt of compound of formula V, Va or VEI may be prepared by any standard method of contacting the compound of formula V, Va or VIII with an acid, for example inorganic acid like hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like or organic acid like oxalic acid, citric acid, succinic acid, cinnamic acid, p-toluenesulfonic acid and the like. As used herein, "alkyl" may be any straight, branched, or cyclic alkyl group of Cl to C6 atoms, optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4-bis(trifluoroalkyl), 2,6-bis(trifluoroalkyl), -CHO, -COOR9, wherein R9 may be alkyl, aryl or heteroaryl.
As used herein, "alkenyl" may be any straight, branched, or cyclic alkyl group of Cl to C6 atoms, optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4-bis(trifluoroalkyl), 2,6-bis(trifluoroalkyl), - CHO, -COOR9, wherein R9 may be alkyl, aryl or heteroaryl.
As used herein, "aryl" may be a mono-, bi- or polycyclic aromatic system, for example phenyl, naphthyl, optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4-bis(trifiuoroalkyl) or 2,6- bis(trifluoroalkyl), -CHO, -COOR9, wherein R9 may be alkyl, aryl or heteroaryl.
As used herein, "heteroaryl" may be a mono-, bi- or polycyclic aromatic system containing one or more hetero atom which may be same or different, for example quinolinyl, isoquinolinyl, pyridinyl, indanyl, fluorenyl, oxazolyl, pyrazinyl, thienyl, quinazolinyl, benzimidazolyl and the like optionally substituted with one or more electron withdrawing groups selected from nitro, halo, cyano, 4-trifluoroalkyl, 2,4- bis(trifluoroalkyl) or 2,6-bis(trifluoroalkyl), -CHO, -COOR9, wherein Rg may be alkyl, aryl or heteroaryl.
As used herein, "hetero atom" may preferably be selected from N, O, S or P,
The base used may be selected from an alkoxide, wherein the alkyl residue is Cl to C6 linear, branched or cyclic alkyl and the counter ion is an alkali or alkaline earth metal; alkali or alkaline earth metal oxide, hydroxide, carbonate or bicarbonate or an amine base. The amine base may be selected from aliphatic or aromatic amines, cyclic or acyclic amines, for example isoquino lines, quino lines, dialkylarylamines, pyridine, substituted pyridines. The base may be selected from moderate bases that do not favor the formation of bisalkoxides thus providing control over the derealization of the primary alcohol group of the diol.
The ether derivative compounds represented by a compound of formula V or Va can cyclize to form citalopram or enantiomers thereof. When the diol compound, viz., a compound of formula IV or IVa is used in enantiomeric form, derivatized to form an ether derivative thereof, a compound of formula V or Va, it cyclizes stereoselectively to afford enantiomerically pure citalopram.
In a preferred embodiment, the group R is:
, wherein one or more of a, b and c may be carbon or hetero atom which may be same or different, P and Q may be selected from electron withdrawing groups like NO2, CF3, CN, halogen, COOR9, CHO and the like, wherein R9 is alkyl, aryl or heteroaryl.
In another preferred embodiment the compound of formula RX is selected from the group consisting of the following compounds:
hi one embodiment the present invention provides a process for preparation of racemic l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile comprising reacting racemic 4-[4-(dimethylamino)-l-(4-fluorophenyl)-l- liydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile5 with a compound of formula RX, in presence of a base. Preferably the compound of formula RX is dichloronitrobenzene. In another embodiment the present invention provides a process for preparation of enantiomeric l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile comprising reacting enantiomeric 4-[4-(dimethylammo)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, with a compound of formula RX, in presence of a base. Preferably the compound of formula RX is dichloronitrobenzene.
In another preferred embodiment the present invention provides a process for preparation of (S)-(+)- 1 -[3-(dimethylammo)ρropyl] - 1 -(4-fluorophenyl)- 1 ,3 -dihydro-5 -isobenzofuran carbonitrile comprising reacting (S)-(-)-4-[4-(dimethylamino)-l -(4-fluorophenyl)- 1- hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, with a compound of formula RX, in presence of a base. Preferably the compound of formula RX is dichloronitrobenzene.
hi a particularly preferred embodiment the present invention provides a process for preparation of (S)-(+)-l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile comprising reacting (S)-(-)-4-[4-(dimethylamino)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile with 2,5- dichloronitrobenzene, in presence of a base to form a compound of formula VHt,
Formula VIII and cyclization of compound of formula VM.
The process of the present invention may be carried out in any suitable solvent. Examples of solvents that may be used are alcohol solvents like methanol, ethanol, t-butanol, polyethyleneglycol; ketone solvents like acetone, methyl iso-butyl ketone; ether solvents like tetrahydrofuran, dioxane; ester solvents like ethylacetate, butylacetate; amide solvents like dimethylformamide, dimethylacetamide; nitrile solvents like acetonitrile; dipolar aprotic solvents like dimethylsulfoxide, sulfolane; hydrocarbon and aromatic hydrocarbon solvents having a boiling point greater than 70°C.
The process of the present invention can be carried out in a suitable solvent with a base at temperature ranging from ambient to the reflux temperature of the selected solvent. The reaction may be completed in 0.5 to 40 hours, preferably 0.5 to 20 hours depending on the selected solvent and base.
In a typical procedure, the reaction may be worked-up by quenching by addition of 2 to 10 volumes, preferably 3 to 8 volumes of water to the reaction solvent, depending on the product solubility in the selected solvent, at temperature between the range of O0C to 100°C, preferably 20°C to 600C. The reaction mixture may be extracted with a suitable water-immiscible solvent like toluene, ether, ethylacetate.
If desired, 1 -[3-(dimethylamino)propyl]- 1 -(4-fluorophenyl)- 1 ,3-dihydro-5-isobenzofuran carbonitrile may be converted to a pharmaceutically acceptable acid addition salt thereof by treatment with organic or inorganic acid. Examples of organic acids are oxalic, fumaric, succinic mandelic, benzoic, p-toluenesulfonic acid and the like. Examples of inorganic acids are hydrobromic, hydrochloric, sulfuric, phosphoric, nitric and the like. The preparation of salt formation may be carried out in a solvent like acetone, water, methanol, isopropanol, dimethylformamide or mixture thereof.
The worked out examples given below illustrate the process and not to be construed as limiting. EXAMPLES
Example 1
Preparation of citalopram oxalate To a solution of 10 gm of (RS)-(±) 4-[4-(dimethylamino)-l-(4-fluorophenyl)-l-hydroxy- l~butyl]-3-(hydroxymethyl)-benzonitrile in 50 ml of dimethylsulfoxide (DMSO) at room temperature was added 12 gm of anhydrous K2CO3 and 6.73 gm of 2,5- dichloronitrobenzene was added to the above reaction mixture at room temperature and stirred at 1000C for 15 hours. To the reaction mixture, 250 ml of water was added and extracted with toluene, the toluene layer was washed with water and 5% sodium hydroxide solution and after acid base treatment yielded an oily product. The oil was dissolved in 40 ml of acetone at 30°C and 3.4 gm of oxalic acid dihydrate was added to it, stirred, cooled, filtered and dried at 6O0C. Dry wt: 7.8 gm.
Example 2
Preparation of (S)-(+)-citalopram oxalate
To a solution of 6 gm of (S)-(-)-4-[4-(dimethylamino)-l-(4-fluorophenyl)-l -hydroxy- 1- butyl]-3-(hydroxymethylbenzoate)-benzonitrile in 60 ml tetrahydrofuran (THF) was added 4.33 gm of potassium tertiary butoxide at 0-100C and stirred for 30 minutes. A solution of 4.04 gm of 2,5-dichloronitrobenzene in 30 ml THF at 0-100C was added to it and stirred for 10-15 hours at room temperature, followed by addition of 250 ml of water. The reaction mixture was extracted with toluene, the toluene layer was washed with water and 5% sodium hydroxide solution and after acid base treatment yielded an oily product. The oil was dissolved in 16 ml of acetone at 3O0C and 1.75 gm of oxalic acid dihydrate in 8 ml acetone was added to it, stirred, cooled, filtered and dried at 6O0C to get the oxalic acid salt of (S)-(+)-l-[3-(dimethylamino) propyl]- 1 -(4- fluorophenyl)- 1,3- dihydro-5-isobenzofuran carbonitrile. Dry wt: 4.3 gm, [α]D = +11.8° ( c=l, methanol). Chiral HPLC: R-isomer content: 0.64% Example 3
Preparation of (S)-(+)-citalopram oxalate
To a solution of 6.0 gin of (S)-(-)-4-[4-(dimethylamino)-l-(4-fluorophenyl)-l -hydroxy- 1- butyl]-3-(hydroxymethyl)-benzonitrile in 30 ml of DMSO at room temperature was added 7.3 gm of anhydrous K2CO3 and 4.04 gm of 2,5-dichloronitrobenzene was added to the above reaction mixture at room temperature and stirred at 100°C for 15.0 hours. To the above reaction mixture, 120 ml of water was added, and extracted with toluene. The toluene layer was washed with water and 5% sodium hydroxide solution and after acid base treatment yielded an oily product. The oil was dissolved in 16 ml of acetone at 30°C and 1.9 gm of oxalic acid dihydrate in 8 ml of acetone was added to it, stirred, cooled, filtered and dried at 60°C.
Dry wt: 4.1 gm, [α]D = +12.62° ( c=l, methanol).
Chiral HPLC: R-isomer content: 0.2%
Example 4
Preparation of (S)-(+)-citalopram oxalate
To a solution of 64 Kg of (S)-(-)-4-[4-(dimethylamino)-l-(4-fluorophenyl)-l -hydroxy- 1- butyl]-3-(hydroxymethylbenzoate)-benzonitrile in 300 lit DMSO was added 77.48 Kg of anhydrous K2CO3 and 43.06 Kg of 2,5-dichloronitrobenzene at room temperature and stirred for 16 hours at 100-105°C. To the reaction mixture 3000 ml of water was added at about 3O0C. The reaction mixture was extracted with toluene, the toluene layer was washed with water and 5% sodium hydroxide solution and after acid base treatment yielded an oily product. The oil was dissolved in 510 lit of isopropanol at about 30°C and 20.4 lit water added, stirred for 10 minutes and 20.8 Kg of oxalic acid dihydrate was added and heated to about 70-75°C, stirred, charcolised, cooled and filtered. The filtrate was cooled to 5-10°C slowly and the resultant solid was filtered, dried at 60°C and micronised to get the oxalic acid salt of (S)-(+)-l'-[3-(dimethylamino) propyl]-l-(4- fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile. Dry wt: 61.5 Kg, [α]D = +13.85° ( c=l, methanol). Chiral HPLC: R-isomer content: 0.38%. Purity by HPLC: 99.25%.
Example 5 Preparation of S-(-)-4-[4-(dimethyIamino)-l-(4-fluorophenyl)-l-hydroxy-l-butyl]-3- (2-nitro-4-chlorophenoxymethyI)-benzonitriIe hydrochloride
To a solution of 5.6 gm of (S)-(-)-4-[4-(dimethylamino)-l-(4-fluorophenyl)-l -hydroxy- 1- butyl]-3-(hydroxymethyl)-benzonitrile in 85 ml THF was added 2.02 gm of potassium tertiary butoxide at 0-100C and stirred for 10 min. 3.14 gm of 2,5-dichloronitrobenzene was added to the reaction mixture at 0-100C and stirred for 10-15 hrs at RT (30-350C), solvent distilled under vacuum and 40 ml of water was added, and extracted with toluene, toluene layer was washed with water and 10% sodium hydroxide solution and distilled to get an oily product, which is purified by column chromatography using silica gel and ethylacetate, Wt: 500 mg.
The above oily product was dissolved in 10 ml of isopropanol (IPA) at 3O0C and 2.0 ml of IP A-HCl was added, stirred and solvent distilled under vacuum and crystallized in IPA to get (-)-4- [4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(2-nitro-4- chlorophenoxymethyl)-benzonitrile hydrochloride whose structure was confirmed by IR, NMR and Mass spectral data. Dry wt: 300 mg, [α]D = - 46.8° ( c=l, methanol).
Analysis calculated for C26H26N3O4C12F: C,58.44; H,4.90; N,7.86; found: C.57.42; H,4.65; N,7.33.
1HNMR (400.13 MHz, DMSO-dό) δl.42-1.43 (broad m, IH); 1.75-1.76(broad m,lH); 2.32-2.47(m, 2H); 2.70(s ,6H); 3.00-3.13(m, 2H); 5.03(d, J= 14.01 Hz, IH); 5.43(d, J= 14.04 Hz5IH); 6.43(s,lH); 6.52(d, J= 9.09Hz, IH,); 7.18(t, 8.71 Hz, J2 =5.41 Hz , 2H); 7.54(dd, J1= 8.97 Hz, J2 =2.63 Hz, IH); 7.90(s, IH); 7.96(d, J= 8.25 Hz,lH); 8.03(d, J= 8.25 Hz, IH,); 8.08(d, J= 2.63 Hz, IH); 10.36(s, IH). 13CNMR (100.61 MHz, DMSO-d6) 618.44 (t); 38.87 (t); 41.86 (2q); 56.47 (t); 67.83 (t); 76.63(s); 110.49(s); 114.84(2d, JH21.23 Hz); 116.11(d); 124.93(d); 118.48(s); 124.17(s); 127.57(d); 127.88(2d, J=8.02 Hz); 130.99(d); 131.31(d); 133.84(d); 136.47(s); 139.55(s); 140.89[s(d, J=2.80 Hz)]; 149.27(s); 149.45(s); 160.91[s(d, J=243.67 Hz)].
Mass: CI Mode, M+=498.20(0.87%); (M-173) =325.30(100.0%).
IR (KBr): cm-1 735.02, 747.45; 1162.70, 1230.44; 1507.93, 1603.51; 1283.12, 1528.82; 2226.34; 2935.53, 3039.88, 3062.31; 3249.93.
Example 6
Preparation of (S)-(+)-citalopram
To a solution of 100 mg of (S)-(-)-4-[4-(dimethylamino)-l-(4-fluorophenyl)-l-hydroxy- l-butyl]-3-(2-nitro-4-chlorophenoxymethyl)-benzonitrile hydrochloride in 2.0 ml of
DMSO was added 64.5 mg of potassium carbonate at 30-350C and stirred for 30 min at
95-1000C. After reaction completion which is monitored by TLC, 40 ml of water was added, and extracted with toluene, toluene layer was washed with water and 10% sodium hydroxide solution and distilled out toluene to get an oily product. Wt: 65.0 mg
Chiral HPLC: S-isomer content: 100%.
1HNMR (400.13 MHz, CDCl3) δl.27-1.38 (m,lH); 1.41-1.53 (m ,1H); 2.13(s, 6H);2.09-
2.25(m, 4H); 5.15(d, J= 12.96Hz, IK); 5.19(d, J= 12.96Hz, IH); 6.98-7.02(m, 2H); 7.38-
7.49(m, 4H); 7.58(d, J= 7.77Hz, IH).
Given below in Table I is the comparison between (S)-(+)-citalopram oxalate prepared by:
A] the prior art process using the methanesulfonyl ester derivative (Experiments A(I),
A(2) and A(3)) and B] the process of the present invention using the ether derivative compound VIII (Experiments B(I), B(2) and B(3)): Table I
Experiment A(I): To a solution of 16 gm of (S)-(-)-4-[4-(dimethylamino)-l-(4-fluorophenyl)-l-hydroxy-l- butyl]-3-(hydroxymethylbenzoate)-benzonitrile in 128 ml dichloromethane was added 14.2 gm of triethylamine, stirred and cooled and 8.0 gm of methanesulfonylchloride was added at below 100C and stirred at less than 100C for 1.0 hr. To the reaction mixture 65 ml of water was added and extracted with dichloromethane. The dichloromethane layer was washed with water and distilled and dissolved the material in toluene, the toluene layer was washed with water and distilled to get an oily product. The oil was dissolved in 50 ml acetone and 5.12 gm of oxalic acid dihydrate in 50 ml acetone was added to it at room temperature, stirred and cooled. The filtrate was cooled to 5-100C slowly and the resultant oxalate salt was filtered, dried at 6O0C and purified by dissolving in 420 ml acetone, heated to reflux temperature, stirred to get clear solution, charcolized and distilled to a residual volume of 75 ml, cooled to 5-10°C slowly and the resultant solid was filtered, dried at 6O0C to get the oxalic acid salt of (S)-(+)-l-[3-(dimethylamino) propyl]- l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile. Dry wt : 9.4 gm [α]D = +13.1° ( c=l, methanol).
Chiral HPLC: R-isomer content: 1.04%. Purity by HPLC : 99.59%.
Experiments A(2) and A(3) have been carried out in similar way as in Experiment No. A(I). Comparative Experiments A(I), A(2) and A(3) have been carried out according to the teaching of prior art, United States Patent No. Re 34712, which is incorporated herein by reference.
Experiment B(I):
To a solution of 16 gm of (S)-(-)-4-[4-(dimethylamino)- l-(4-fluorophenyl)-l -hydroxy- 1- butyl]-3-(hydroxymethylbenzoate)-benzonitrile in 75 ml DMSO was added 19.3 gm of anhydrous K2CO3 and 10.8 gm of 2,5-dichloronitrobenzene at room temperature and stirred for 15 hours at 100-105°C. To the reaction mixture 750 ml of water was added at about 30°C. The reaction mixture was extracted with toluene, the toluene layer was washed with water and 5% sodium hydroxide solution and after acid base treatment yielded an oily product. The oil was dissolved in a mixture of 125 ml IPA and 5 ml water at 30°C and 5.3 gm of oxalic acid dihydrate was added to it, heated to 70-750C, stirred and charcolized to get clear solution, cooled to 5-1O0C slowly and the resultant oxalate salt was filtered, dried at 600C and purified by dissolving in a mixture of 140 ml isopropanol and 5.6 ml water at 3O0C heated to 70-750C, stirred to get a clear solution, cooled to 5-100C slowly and the resultant solid was filtered, dried at 6O0C to get the oxalic acid salt of (S)-(+)-l-[3-(dimethylamino) propyl]- l-(4-fluorophenyl)- 1,3-dihydro- 5-isobenzofuran carbonitrile. Diy wt : 13.3 gm [α]D = +13.2° ( c=l, methanol). Chiral HPLC: R-isomer content: 0.34%. Purity by HPLC : 99.76%.
Experiments B(2) and B(3) have been carried out in similar way as in Experiment No. B(I), which illustrate the process of the present invention, It is evident from the data presented in Table I and the worked out examples, that (S)-(+)- citalopram prepared by the process of the present invention contains R-isomer in the range of 0.00 to 0.38%, whereas (S)-(+)-citalopram prepared by the prior art process of methanesulfonyl ester derivative contains R-isomer in the range of 0.84 to 1.04%.

Claims

Claims:
1) A process for preparation of l-[3-(dimethylammo)propyl]-l-(4-fluorophenyl)-l,3- dihydro-5-isobenzofuran carbonitrile comprising reacting a compound of formula IVa, in the presence of a base with a compound of formula RX,
Formula IVa wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf 10 and OR1, wherein Tf represents trifiuoromethanesulfonyl group, and Rj is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group; further wherein RX is selected such that an intermediate ether derivative, a compound of formula Va formed from said reaction cyclizes to a compound of formula VI,
Formula Va Formula VI and where Z is not a cyano group, conversion of the group Z in the compound of formula VI to a cyano group to form l-[3-(dimethylamino)proρyl]-l-(4-fluorophenyl)-l,3- dihydro-5-isobenzofuran carbonitrile.
>0 ■2) A process for preparation of l-[3-(dimethylamino)propyl]-l-(4-fluoiOphenyl)-l,3- dihydro-5-isobenzofuran carbonitrile comprising reacting 4-[4-(dimethylamino)-l-(4- fluorophenyl)-l-hydroxy-l-butyl]-3-(hydroxymethyl)-benzonitrile, in the presence of a base, with a compound of formula RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN, OTf and OR1, wherein Tf represents trifluoromethanesulfonyl group, and Ri is optionally substituted alkyl; further wherein RX is selected such that an intermediate ether derivative, a compound of formula V formed from said reaction,
cyclizes to l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5- isobenzofuran carbonitrile.
3) The process as claimed in claim 2 wherein, racemic l-[3-(dimethylamino)propyl]-l-
(4-fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile is formed by reacting racemic 4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3- (hydroxymethyl)-benzonitrile with a compound of formula RX.
4) The process as claimed in claim 2 wherein, (S)-(+)-l-[3-(dimethylamino)ρropyl]-l-(4- fluorophenyl)-l,3-dihydro-5-isobenzofuran carbonitrile is formed by reacting (S)-(-)- 4- [4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(hydroxymethyl)- benzonitrile with a compound of formula RX. 5) The process as claimed in claim 2 wherein, in the compound of the formula RX,- the
group R is , wherein one or more of a, b and c may be carbon or hetero atom which may be same or different, P and Q may be selected from electron withdrawing groups like NO2, CF3, CN, halogen, COORg, CHO and the like, wherein R9 is alkyl, aryl or heteroaryl.
6) The process as claimed in claim 2 wherein, the compound of formula RX is selected from the group consisting of the following compounds:
7) A compound of formula Va, or acid addition salt thereof,
Formula Va wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and Z is a cyano group or a group that may be converted to a cyano group.
8) A compound of formula V, or acid addition salt thereof,
Formula V
wherein R is selected from alkyl, alkenyl, aryl and lieteroaryl which may be optionally substituted with electron withdrawing groups.
9) A process for preparation of a compound of formula Va, comprising reacting a compound of formula IVa, in the presence of a base with a compound of formula RX,
Formula IVa Formula Va wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I5 CN, OTf and OR1, wherein Tf represents trifiuoromethanesulfonyl group, and Ri is optionally substituted alkyl, Z is a cyano group or a group that may be converted to a cyano group.
10) A process for preparation of a compound of formula V,
Formula V
comprising reacting 4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl]-3-
(hydroxymethyl)-benzonitrile, in the presence of a base, with a compound of formula
RX, wherein R is selected from alkyl, alkenyl, aryl and heteroaryl which may be optionally substituted with electron withdrawing groups and X is selected from F, Cl, Br, I, CN,
OTf and OR1, wherein Tf represents trifluoromethanesulfonyl group, and R1 is
10 optionally substituted alkyl.
11)4- [4-(Dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl] -3 -(2-nitro-4- chlorophenoxymethyl)-benzonitrile, a compound of Formula VIII, or acid addition salt thereof,
Formula VIII
12) (S)-4-[4-(dimethylamino)- 1 -(4-fluorophenyl)- 1 -hydroxy- 1 -butyl]-3 -(2-nitro-4- chlorophenoxymethyl)-benzonitrile, or acid addition salt thereof.
>0 3) The hydrochloride salt of the compound as claimed in claim 12.
EP05815687A 2004-08-23 2005-08-12 "process for preparation of citalopram and enantiomers" Withdrawn EP1797060A2 (en)

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EP1877394A1 (en) * 2005-04-04 2008-01-16 Jubilant Organosys Limited Process for the preparation of escitalopram or its acid addition salts
WO2008059514A2 (en) * 2006-07-31 2008-05-22 Cadila Healthcare Limited Process for preparing escitalopram
AU2010270797B2 (en) 2009-07-08 2015-03-19 Dermira (Canada), Inc. TOFA analogs useful in treating dermatological disorders or conditions
KR101842425B1 (en) 2015-10-27 2018-05-14 주식회사 경보제약 New process for preparing Citalopram and Escitalopram
KR102134179B1 (en) * 2018-09-17 2020-07-16 (주)유케이케미팜 A New method for the production of citalopram and escitalopram using carbonates

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US7790935B2 (en) 2010-09-07
WO2006021971A3 (en) 2006-07-13
US20100249437A1 (en) 2010-09-30
KR101166280B1 (en) 2013-11-27
ES2285972T1 (en) 2007-12-01
WO2006021971A2 (en) 2006-03-02
KR20070083586A (en) 2007-08-24
US7964742B2 (en) 2011-06-21
DE05815687T1 (en) 2007-10-18
US20090326249A1 (en) 2009-12-31

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